The present invention relates to a permanent magnet motor system and related circuit for controlling the operation of electric motor systems.
In low cost electronic drive design for motors it is cost advantageous to use a minimum number of power switching devices. In addition it is lowest cost to use only “low side” switching, that is, switches that sink current directly to ground thus not needing expensive gate drive circuits.
In consequent pole PM machines this architecture often creates an issue with the inactive winding. The motor acts as a transformer so the potential exists for the inactive winding to conduct current and create negative torque (losses). To date the only solution for this issue is to use a single top side switch with gate driver circuit negatively affecting system cost. Another alternative is to only use bottom side switches and change the traditional diode flyback clamp to an RC type (the diode clamp will allow inactive winding current resulting in low efficiency). An RC type snubber circuit prevents dc current in the inactive winding while replacing the diode in its role as flyback protector for the switch. However, with this approach much of the energy captured by the flyback RC snubber is dissipated as heat—again, energy losses.